docs: Replace custom version banner with PyData theme built-in

Remove the hand-rolled dev-version warning (raw HTML in index.rst and
citations.rst, JS detection in custom.js, and CSS in custom.css) now
that show_version_warning_banner from PyData Sphinx Theme covers the
same use case. Also exempt switcher.json from the docs/_*/ gitignore
rule so force-add is not needed.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Author: kratsg

.gitignore

@@ -9,6 +9,7 @@ docs/config.rst
 docs/gh-pages
 docs/pyhf.*.rst
 docs/_*/
+!docs/_static/switcher.json
 *.py[co]
 __pycache__
 *.egg-info

docs/_static/css/custom.css

@@ -2,45 +2,3 @@
 .wy-nav-content {
     max-width: 1200px !important;
 }
-
-/* version warning badge */
-#dev-version {
-  display: none;
-}
-
-#dev-version.version-warning {
-  display: block;
-}
-
-p.version-warning {
-  position: sticky;
-  top: 10px;
-
-  margin: 10px 0;
-  padding: 5px 10px;
-  border-radius: 4px;
-
-  letter-spacing: 1px;
-  color: #fff;
-  text-shadow: 0 0 2px #000;
-  text-align: center;
-
-  background: #900 repeating-linear-gradient(
-    135deg,
-    transparent,
-    transparent 56px,
-    rgba(255, 255, 255, 0.35) 56px,
-    rgba(255, 255, 255, 0.35) 112px
-  );
-}
-
-p.version-warning a {
-  color: #fff;
-  text-decoration: none;
-  border-bottom: 1px dotted #fff;
-}
-
-p.version-warning a:hover {
-  border-bottom-style: solid;
-}
-/* -------------------------- */

docs/_static/js/custom.js

@@ -1,10 +1,6 @@
 Use and Citations
 =================
 
-.. raw:: html
-
-   <p id="dev-version"><strong>Warning:</strong> This is a development version and should not be cited. To find the specific version to cite, please go to <a href="https://pyhf.readthedocs.io/">ReadTheDocs</a>.</p>
-
 Citation
 --------
 

docs/citations.rst

@@ -292,7 +292,6 @@ def setup(app):
 ]
 
 html_js_files = [
-    "js/custom.js",
     (
         "https://views.scientific-python.org/js/plausible.js",
         {"data-domain": "pyhf.readthedocs.io", "defer": "defer"},

docs/conf.py

@@ -22,10 +22,6 @@
    release-notes
    contributors
 
-.. raw:: html
-
-   <p id="dev-version"><strong>Warning:</strong> This is a development version. The latest stable version is at <a href="https://pyhf.readthedocs.io/">ReadTheDocs</a>.</p>
-
 ..
   Comment: Splice the JupyterLite example into the README by looking for a particular comment